Sprinkle zucchini lightly with salt. Transfer to a colander; drain for 15 minutes. Pat dry with paper towels. Preheat oven to 400°F.

Meanwhile, on a large piece of lightly floured parchment paper, roll pie dough to a 12-inch circle. Transfer parchment and dough to a large baking sheet; set aside.

For ricotta filling, in a medium bowl whisk together ricotta, Parmesan, mozzarella, garlic, 1 tsp. of the olive oil, lemon peel, lemon juice, salt, and pepper. Using a spatula, spread over dough, leaving a 1 1/2 inch border. Top with squash rounds. Drizzle with remaining olive oil. Gently fold over pastry edge, pleating as necessary.

In a small bowl whisk egg yolk and 1 tsp. water. Lightly brush pastry edges with egg mixture. Transfer galette to oven. Bake 35 to 40 minutes or until edges are golden brown. Sprinkle with dill weed, if desired. Serve warm or at room temperature.